1.7 Microbial diversity in general

Micro-organisms exist in every conceivable place on Earth, even in
extreme environments. The tropics are considered to be richer in
microbial species diversity than the temperate zones, but deserts may feature an
equal amount, if not more, microbial diversity, and microbial communities can be
found on rocks and within deep rock crevices (e.g. Staley et al.,
1982). Temperature may be the only limitation as to where they can and cannot
exist and/or function (Hunter-Cevera, 1998).

The conservativeestimate
is
that there are 1.5 million species of fungi on Earth, of which only
120,000 species have been isolated or described
(Hawksworth, 1997, 2001; Hawksworth & Lücking, 2017). The former estimate was
made by comparing the number of species of fungi and vascular plants described
for particular geographic regions. For example, in the British Isles there are
about six times more species of fungi than species of vascular plants.
Extrapolating this ratio to the 270,000 species of vascular plants in the world
gives an estimate of 1,620,000 fungi. Now, this figure needs to be corrected (to
1,504,800) to account for the double counting of fungal species resulting from
the practice of giving separate specific names to the asexual and sexual stages
of some fungi (because it may not be known that the two reproductive stages
belong to the same fungus).
In recent years molecular approaches to species recognition, together with the
recognition of new habitats, hyper-diverse environments and unstudied
collections have prompted revision of this conservative
estimate of fungal diversity. Hawksworth & Lücking (2017) conclude that the
range 2.2 to 3.8 million species of fungi on Earth is a better
estimate. They point out that this means that ‘…at best just 8%,
and in the worst case scenario just 3%...’ of the world’s fungi have been
formally described and named so far. You might well ask: ‘Where are the other 92
to 97% of undescribed fungi?’

Part of the answer to that question is that there are not many mycologists in
the world today and not much work has been done in several unique geographical
regions or habitats. Many ‘missing fungi’ may be associated with tropical
forests, for example. Insects may be another large source of missing fungi as
many fungi are already known to be associated with insects. Finally, many
missing fungi may be discovered in specialised habitats which have not yet been
explored at all, or have been only poorly investigated. The rumen and hindguts
of herbivorous animals and the inner surfaces of Antarctic rocks do not sound
like very promising habitats, but they are examples of habitats
that have, unexpectedly, already yielded novel fungi.

Wherever they occur, fungal communities are very diverse metabolically,
physiologically and taxonomically (Bass & Richards, 2011; Money, 2014). Given
the benefits that man has derived from the fungi we know about, it is
surprising, and disappointing, that more efforts have not been made to seek out
these still unisolated fungi.

Resources Box

About the diversity of fungi

We do not intend to expand further on the topic of
fungal biodiversity here because we prefer to concentrate on other
particular aspects of the fungal contribution to the soil community, but
if you wish to investigate fungal diversity now
CLICK HERE to see our page of recommended literature references.